Electrical resistivity

Electrical resistivity (also known as specific electrical resistance) is a measure indicating how strongly a material opposes the flow of electric current; if the resistivity of the material is small, that means that material is effective to carry electrons.

The resistivity of a material is usually denoted by the lower-case Greek letter rho (ρ) and is given by RS/l, where R is the resistance of a uniform specimen of the material, having a length l and a cross-section area S. The units of ρ are ohm meters. Its reciprocal quantity is electrical conductivity.

Also the resistivity is the magnitude of the electric field divided by the magnitude of the current density[?].

In general, electrical resistivity of metals increases with temperature, while the resistivity of semiconductors decreases with temperature.

Some materials lose all electrical resistivity under certain conditions; this effect is known as superconductivity.

The table of resistivity for various materials (at 20 degree):

Material	Resistivity (Ohm-meters)
Silver	1.59 x 10-8
Copper	1.7 x 10-8
Gold	2.44 x 10-8
Aluminum	2.82 x 10-8
Tungsten	5.6 x 10-8
Iron	10 x 10-8
Platinum	11 x 10-8
Lead	22 x 10-8
Nichrome[?] (A nickel-chromium alloy commonly used in heating elements)	1.50 x 10-6
Carbon	3.5 x 10-5
Germanium	0.46
Silicon	640
Glass	1010 to 1014
Hard rubber[?]	approximately 1013
Sulfur	1015
Quartz (fused)	75 x 16